1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for improving reliability of electrical connections at radio frequency (RF). Particularly, embodiments of the present invention relate to apparatus and methods for improving reliability of RF grounding at high temperatures.
2. Description of the Related Art
A substrate support having an embedded RF electrode is usually used in a plasma enhanced process, for example, plasma enhanced physical vapor deposition (PECVD). The substrate support generally has a non-conductive body, such as a ceramic body. One or more heating element may be included in the substrate support to provide heating during processing. The RF electrode is typically connected to a RF power source through a series of metal parts including clamps and straps to accommodate some relative motions caused by thermal expansion. The clamps and straps are generally made of metals with minimal resistivity (copper) and with a coating (of gold or nickel) to prevent oxidation.
However, many issues arise from traditional RF connection, particularly when the substrate support is heated to a temperature higher than 400° C. or the RF power is above 1000 W. The coating on the clamps and straps tend to fail when the temperature of the clamps and straps is higher than 250° C. causing oxidation. The oxidation on the surface of the clamps and straps leads to arcing in the chamber, thus negatively affect the processing. High temperature may also cause the clamps and straps to lose flexibility needed to maintain electrical contact between the RF power source and the RF electrode. The clamps and straps may even break at high temperature.
Therefore, there is need for apparatus and methods to improve reliability of electrical contact between an RF electrode and a RF power source.